Nev, As the saying goes. Peter is being robbed to pay Paul.H2O robs CO2 to pay the bank—and then the bank (climate models) wonders why CO2's potential earnings have mysteriously vanished. Thanks for posting the classic top-of-atmosphere spectra—but it doesn’t prove what is often portrayed.
Yes, the CO2 and (H2O) dip shows that less IR escapes to space in that band, and that radiation originates from colder, higher altitudes. That’s expected.But this chart does not show that CO2 at the surface is emitting photons. (aka Back radiation). In fact:
In the lower troposphere, CO2 is colliding billions of times per second with surrounding molecules.
Those collisions quench vibrational modes before photon emission can occur. A process called collisional de-excitation (CDE) as we have discussed before.
Only at higher altitudes, where air is thin and collisions are rare can radiative de-excitation (RDE) occur and produce measurable emission.
So no, a “hole” in the CO₂ emission band from space doesn’t mean radiation dominates at the surface—it means CO₂ absorbs IR and re-emits it at higher, colder levels. Via collisions the absorbed energy is redistributed out over other wavelengths. That’s entirely consistent with a collision-dominated lower troposphere and a radiative upper atmosphere.
Your unicorn analogy is cute, but physics beats memes every time. Note. In the lower troposphere, water vapor absorbs most of the thermal radiation in bands that overlap with CO2, particularly in the 13–17 µm range. So in humid air, H2O outcompetes CO2 for IR absorption.
Once H2O condenses into cloud droplets, it becomes a grey body emitter, radiating more like a blackbody according to Planck’s law, not discrete molecular lines that you think. That means the emitted energy is spread across a broad range of wavelengths rather than narrow absorption bands.
So yes—water not only dominates absorption, but when condensed, it also broadens the spectrum of outgoing radiation via thermal radiation. Not RDE.
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